Apparatus for exposing a pulverulent pasty or liquid material to the action of a controlled atmosphere

ABSTRACT

The apparatus comprises a main conveyor screw which rotates within a main bore having at least one lateral slot which communicates with an exposing chamber. The latter is maintained under vacuum or receives a treating gas. A returning conveyor screw rotates in a bore situated below the exposing chamber and which communicates with the main bore and with the exposing chamber in order to return into the former the material which may have been thrown into the latter by the main screw. The material is introduced into the main bore by a feed device, as for instance a feed screw, so arranged as to form an airtight seal isolating the main bore from the outer atmosphere. In the same manner the material treated is withdrawn from the main bore by an outlet device also forming an airtight seal. More particularly in the case of pasty or plastified materials the airtight seal may be obtained by increasing the diameter of the core of the screws in order to compress the material in the form of a plug between the successive turns.

United States Patent lnventor Pierre Poncet 12 bis, Rue Trarieux, Lyon,France Appl. No. 823,689 Filed May 12, 1969 Patented Mar. 30, 1971APPARATUS FOR EXPOSING A PULVERULENT PASTY OR LIQUID MATERIAL TO THEACTION OF A CONTROLLED ATMOSPHERE Primary Examiner-Robert W. JenkinsAtt0rneyAlexander & Dowel] ABSTRACT: The apparatus comprises a mainconveyor screw which rotates within a main bore having at least onelateral slot which communicates with an exposing chamber. The latter ismaintained under vacuum or receives a treating gas. A returning conveyorscrew rotates in a bore situated below the exposing chamber and whichcommunicates with the main bore and with the exposing chamber in orderto return into the former the material which may have been thrown intothe latter by the main screw. The material is introduced into the mainbore by a feed device, as for instance a feed screw, so arranged as toform an airtight seal isolating the main bore from the outer atmosphere.ln the same manner the material treated is withdrawn from the main boreby an outlet device also forming an airtight seal. More particularly inthe case of pasty or plastified materials the airtight seal may beobtained by increasing the diameter of the core of the screws in orderto compress the material in the form of a plug between the successiveturns.

Patented March 30, 1971 3,572,644

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APPARATUS FOR EXPOSING A PULVERULENT PASTY OR LIQUID MATERIAL TO THEACTION OF A CONTROLLED ATMOSPHERE BACKGROUND OF THE INVENTION Thepresent invention relates to an apparatus to expose a pulverulent, pastyor liquid material to the action of a controlled atmosphere and moreparticularly of vacuum. Such an apparatus may be used for degassingplastic substances in an injection or an extrusion machine, foreliminating volatile components from a divided material, for thetreatment of a substance by a gas, etc.

SUMMARY OF THE INVENTION The apparatus according to the presentinvention comprises a main conveyor screw rotating in a substantiallyhorizontal main bore which communicates laterally with an exposingchamber. a feed device supplying the material to be treated to a firstend of the main bore while isolating the latter from the outeratmosphere, an outlet device withdrawing the material from the secondend of the main bore while also isolating the latter from the outeratmosphere, and a returning screw rotating in a substantially horizontalbore disposed below the exposing chamber and which communicateslaterally with the said chamber and with the main bore so as to returninto the latter the material being treated which has passed from thesaid main bore into the exposing chamber or into the bore of the saidreturning screw. 1 I

More particularly when the material is to be submitted to the action ofvacuum, the communication between the main bore, the exposing chamberand the bore of the returning screw is preferably in the form ofan'elongated slot extending along a substantial portion of the length ofthe main bore. The returning screw may then propel the material in thereverse direction with respect to the main screw so as to realize arecycling effect. In the case of a gas the exposing chamber may be inthe form of two spaces respectively communicating with one and the otherend of the main bore thegas being supplied to one of these spaces so asto circulate along themain bore and to issue therefrom through the otherspace,

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS Referring to FIGS. 1 and 2 the apparatus comprises a massivebody 1 formed with five substantially parallel bores, respectively la,1b, Ic, Id and 1e. As illustrated bore lb which I has the largestdiameter, is disposed axially with respect to body I, bore la and Itbeing situated respectively above and below bore la and on the same sideof the vertical axial plane of body I, while bores ld and le aredisposed close to each other and to bore lb on the other side of thesaid plane, bore ld having its axis substantially in the horizontalaxial plane of body I and bore is being situated above that plane.

A feed screw 2 (FIG. 2) is rotatably mounted in bore la.

Starting from the right, the core of this screw comprises a divergingfrustoconical section and a cylindrical section. This core supports ascrew thread 2a of uniform pitch but of varying radial height, having anouter diameter substantially equal to the diameter of bore la. Screw 2extends towards the right in the form of a solid cylindrical portion 2balso having a diameter substantially equal to the diameter of bore Ia.This portion 2b is integral with a driving shaft 2c.

Body 1 is formed with a substantially vertical radial canal If whichopens downwardly into bore la in the vicinity of the right end of screw2 in FIG. 2. The upper or outer end of this canal If is connected withan appropriate hopper such as diagrammatically illustrated at 3. Theleft end of bore 10 communicates with bore 1b through a transverse canallg.

Another conveyor screw or main degassing screw 4, is rotatably mountedin the larger bore or main bore lb. Starting from'the right in FIG. 2.the core of this screw comprises a converging frustoconical portionfollowed by a cylindrical portion, and finally a diverging frustoconicalportion. This core carries a screw thread 40 of uniform pitch, but ofvarying radial depth and having an outer diameter substantially equal tothe diameter of bore lb. Screw 4 extends outwardly in the form of acylindrical portion having substantially the same diameter as bore Ib soas torotate therein with a quite small clearance, this portion beingintegral with an outer shaft 4b mechanically connected with anappropriate driving gearing, not shown. As illustrated the cylindricalportion may be formed with a helical groove in order to prevent anyleakage of the material treated.

An inclined canal 1h starts from the right end of the main bore lb andopens into bore 1c. The left end of this bore 1c forms the outlet Ii ofthe apparatus. In the embodiment illustrated this outlet is adapted toreceive an injection nozzle (not illustrated) having a spring-loadedvalve in the conventional manner.

An outlet screw 5 is rotatably disposed within bore 10. The core of thisscrew comprises, starting from the right in FIG. 2, a cylindricalsection and a diverging frustoconical section the larger diameter ofwhich is however smaller than the diameter of bore lc. This core carriesa screw thread 5a of uniform pitch but of varying radial height, andhaving an outer diameter substantially equal to the diameter of bore 1c.The core of screw 5 extends toward the right in the form of a rod orshaft 5b having substantially the same diameter as bore lc, which may berotated by an appropriate gearing (not shown) and axially displaced asfor instance by means of a hydraulic ram in a per se known manner. Shaft5b may for instance comprise a fluted portion slidable through thegrooved bore of a driving gear, while its end is rotatably connectedwith the piston of the ram.

The left end of the core of screw 5 carries a cylindrical head 5c whichacts as a piston within bore 10. This head is formed with an innerchamber in which is disposed a ball valve 6'. This chamber opens on thefree end of head Sc and it communicates with a radial conduit 5dprovided in the diverging frustoconical section of the core of screw 5,close to the larger base thereof. Ball 6 only permits passage of thetreated material from screw 5 towards outlet Ii. As usual in suchvalves, ball 6 is centered by longitudinal ribs which only leave it alimited longitudinal freedom.

As illustrated in FIG. I bores lb, 1d and le are laterally connectedwith each other by an elongated longitudinal passage or slot whichextends along a substantial portion of their length. a

A returning screw 7 is rotatably disposed within bore Id. This screwcomprises a cylindrical core with a screw thread of uniform height andof constant pitch. As illustrated in FIG. I screw 7 is disposed close tothe degassing screw 4. As screws 2 and 4, screw 7extends outwardly onthe right side of the apparatus in FIG. 2 in the form of a shaftconnected with an appropriate driving gearing, not illustrated.

As to bore le, it forms a vacuum chamber void of any conveyorscrew andfor this purpose it is connected through a conduit 8 with an appropriatesource of vacuum, not shown.

In operation a thermoplastic material loaded in hopper 3 is conveyedtowards the left in FIG. 2 by the feed screw 2 which is rotated in theproper direction, as indicated by the arrows. The apparatus beingmaintained at a proper temperature by heating means, not illustrated,the material is plastified and owing to the progressive increase of thediameter of the core of the screw in the final frustoconical sectionthereof, it is highly compressed in the form of a gastight plug betweenthe turns of screw 2 and the wall of bore 10. The compressed materialflows through canal lg into the main bore lb.

The degassing screw 4 conveys the material from the left end of bore lbto the right end thereof. In the portion wherein the core of the screwis cylindrical, the material is no more compressed owing to the increaseof. the volume comprised between two successive turns of the screwthread 5a. It is therefore highly stirred and all its particles aresuccessively exposed to the action of vacuum through the lateral slotwhich connects bores 1b and le with each other.

The material propelled by screw 4 is again compressed in the left-handportion thereof owing to the frustoconical shape of the core and itflows into bore through canal lh.

During the longitudinal displacement of the material in the main borelb, a fraction thereof leaves the corresponding screw 4 in the zonecorresponding to the lateral slot which connects bores lb and le witheach other. This fraction falls into bore 1d and it is conveyed by screw7 towards the left end of the apparatus where it is finally recycledinto bore lb. This recycling enhances the homogeneity of the materialwhen the latter comprises a mixture of components. MOreover the fractionrecycled by screw 7 is exposed to vacuum during a longer time.

The material forced by the main screw 4 into bore 10 is propelledtowards the left by the outlet screw 5. It passes through canal 5d andthrough head 50. The valve of the injection nozzle (not illustrated)adapted to outlet li being closed by its loading spring, this materialaccumulates and pushes screw 5 towards the right in FIG. 2, thecontrolling valve of the hydraulic ram which actuates longitudinallyshaft 5b being set to the position which permits free contraction of theram. when the quantity of plastified material thus accumulated betweenthe injection nozzle and head 65c is deemed sufficient, the hydraulicram is actuated so as to return screw 5 towards the right. The flow ofmaterial from left to right bring prevented by ball 6, head 5c acts asan injection piston in a per se known manner. The material under highpressure opens the spring-loaded valve of the injection nozzle and fillsthe molding cavity of the mold against which this nozzle is applied.

In a modified embodiment the apparatus may comprise two outlet screwsacting in alternate succession, one receiving the plastified materialfrom screw 4 while the other one injects into a mold the charge ofplastified material previously received.

In another modification screw 5 is retained axially at a fixed positionand an extrusion nozzle is adapted to outlet Ii, the treated materialbeing continuously forced through this nozzle under the action of screw5.

In any case the compression of the plastified material at both ends ofthe main screw 4 forms an airtight seal which prevents any air ingressinto the vacuum chamber or bore le.

The apparatus of FIGS. 1 and 2 may be used for the treatment ofpulverulent materials. In such a case the seal at both ends of screw 4is not perfect, but nevertheless the negative pressure maintained inbore la may be quite high. If the material treated is neither to beinjected, nor to be extruded, the outlet 1i may be left open.

The apparatus of FIGS. 1 and 2 may also be used for the treatment ofliquids. In such a case the main screw 4 is preferably rotated at a highspeed in order that the liquid may be maintained against the wall of themain bore lb. The inlet and the outlet of the liquid may be effected bymeans of rotary valves or of pumps.

When screw 4 rotates at a high speed, a substantial fraction of thematerial is thrown into bore 1e. If this material is liable to stick tothe wall of said bore, the latter may be provided with a rotary scraper.

FIG. 3 shows an embodiment wherein cooling tubes 9 have been disposedwithin bore 1e in order to condense volatile components evolved by thematerial treated. The wall of bore lb or the core of screw 4 may then beheated to promote vaporization of these components. If the condensedcomponent is a liquid, the apparatus may be slightly inclined in orderthat this liquid may be collected at one end of bore Id.

In the modification of FIG. 4 the cooling fluid flows through canals 10provided in body 1 around bore 12. Condensation of the volatilecomponents thus takes place on the wall of this bore and if thecondensed product has a tendency to stick to the wall, bore 1e may beequipped with a rotary scraping device comprising for instance a shaft Icarrying scraping blades 12.

FIG. 5 illustrates an arrangement in which an elongated cylindricalmember 13 is axially disposed within bore le, this member being formedwith longitudinal canals 14 for the circulation of a cooling fluid. Thescraping device comprises double blades 15 which rotate in the annularspace between member 13 and the wall of bore le. These blades may becarried by longitudinal rods supported by a rotating plate disposed atone end of bore le, member 13 being only supported by its end remotefrom the rotating plate and the latter being of course carried by anappropriate shaft.

The advantage of the embodiment of FIG. 5 is that if bore lb is heatedeither by heating means or by the material treated, this has noinfluence on the cooling effect of member I3, while with the arrangementof FIG. 4 some heat barrier should be provided in body I between boreslb and le if it is desired to avoid heat losses by conduction.

FIG. 6 illustrates an embodiment particularly adapted to the treatmentof liquids, with screw 4 rotating at a high speed, as above indicated. Alip Ik extends between bores lb and 1e in order to prevent or tominimize liquid projections into bore Ie under the action of centrifugalforce. The liquid expelled from bore lb collects in bore 1d and isrecycled by screw 7. The embodiment of FIG. 6 comprises no feed screwand no outlet screw, the liquid being fed into the apparatus andextracted therefrom by rotary valves or pumps, as above indicated.

In the modification of FIG. 7 the vacuum chamber is no more in the formof a bore, but of a relatively wide inner space I! disposed above themain bore lb and which communicates freely therewith. The apparatuscomprises two returning screws 16 and I7 situated on one and the otherside of this space or chamber, close to bore lb.

It has hitherto been supposed that the apparatus was used for exposing amaterial to the action of vacuum. But it may also be applied forsubmitting a material to the action of a gas. However a difl'iculty thenarises owing to the fact that the gas which then fills bore le is notrenewed and does not circulate in contact with the material beingtreated. This may be avoided by means of the embodiment illustrated inFIG. 8. In this FIG., which corresponds to a section by the planedefined by the axes of bores 1b and Ie, the main screw 4 has beenillustrated with a cylindrical core for the sake of simplicity and alsobecause a gastight seal at both ends of this screw is here of lesserimportance if the treating gas is itself under a pressure substantiallyequal to the outer atmospheric pressure. Also the feed screw and theoutlet screw have been omitted for the sake of simplicity. Alongitudinal partition lm is interposed between the main bore lb andbore Ie which may be described in this case as the gas chamber. Bore leis divided into two individual spaces by a transverse partition In. Thelongitudinal-partition lm has an opening adjacent each end, namely 10and 1p. The gas is supplied through an inlet nozzle lq into theleft-hand portion or elementary space of bore 1e and it leaves theapparatus through an outlet nozzle lr provided in the right-hand portionof the said bore. It therefore flows from left to right through the mainbore lb, as indicated by the arrow, in contact with the material stirredand propelled by screw 4 in the reverse direction between inlet canal lgand outlet canal 1h. Of course the feed of material to screw 4 should besuch that the space defined between the successive turns thereof areonly partially filled.

The returning screw 7 cooperates with the openings and 1p in such manneras to recycle through the latter the material which has passed throughthe former from bore lb into bore 1e. It will be seen that a fraction ofthe treating gas flows through the turns of screw 7 which therefore actsas a short circuit for the main screw 4, but owing to the small diameterof screw 7, this is of minor importance. Furthermore the gas which flowsthrough screw 7 acts on the material recycled by the latter and is nottherefore entirely lost.

In the modification of FIG. 9 bore 1e has been suppressed and the inletand outlet nozzles llq and 1r open directly in front of openings 10 and1p of the longitudinal partition Im. It is obvious that the operation ofthe apparatus remains unchanged, but its dimensions may be reduced withrespect to the case of FIG. 8.

FIG. 10 illustrates a further modification wherein the returning screw 7has a plain central portion and two screwthreaded end portions. Theinlet and outlet nozzles Iq and Ir are thus no more partiallyshort-circuited by screw 7 and the longitudinal partition 1m of FIGS. 8and 9 may be dispensed with, the plain portion of screw 7 playing itsrole. However the material is no more recycled from the left end ofscrew 4 to the right end thereof, the terminal screw-threaded portionsof screw 7 only returning into bore lb the material which wouldotherwise tend to clog the gas passage.

In FIG. 10 both screw-threaded portions of screw 7 are in the samedirection and the screw is rotated so as to propel the material towardsthe left. In the modification of FIG. ll these screw-threaded portionsare of opposed pitch, but in both cases the screw 7 returns into bore lbthe material which would otherwise clog nozzles Iq and In It is to benoted that in the embodiment of FIGS. 1 and 2 the tenninal frustoconicalportions of the core of the main screw 4 may often be dispensed with,the said core being cylindrical along its whole length. The airtightseal required for the operation is then realized at the left end of thefeed screw 2 and at the right end of the outlet screw 5.

Iclaim:

1. An apparatus for exposing a pulverulent, pasty or liquid material tothe action of a controlled atmosphere and more particularly of vacuum,comprising:

a body having a substantially horizontal main bore with a first end anda second end, an exposing chamber communicating laterally with said mainbore, and a substantially horizontal returning bore in lateralcommunication with said exposing chamber and said main bore to receivefrom said exposing chamber the material which passes from said main boreinto said exposing chamber;

a main conveyor screw rotating in said main bore to propel the materialfrom the first end of said main bore to the second end thereof;

a returning conveyor screw rotating in said returning bore to returninto said main bore the material received in said returning bore;

a feed device to feed the material to be treated into the first end ofsaid main bore while forming a substantially airtight seal between saidfirst end and the outer atmosphere; and

an outlet device to withdraw the treated material from the second end ofsaid main bore while also forming a substantially airtight seal betweensaid second end and the outer atmosphere.

2. In an apparatus as claimed in claim 1, said returning conveyor screwpropelling the material being treated in the reverse direction withrespect to said main conveyor screw so as to recycle said material fromthe second end of said main bore towards the first end thereof.

3. In an apparatus as claimed in claim 1, means to cool said exposingchamber so as to condense vapors evolved from the material beingtreated.

4. In an apparatus as claimed in claim I, said body being formed with aninlet bore having a first end and a second end,

with a material receiving inlet canal opening into said first end ofsaid inlet bore, and with a connecting canal to connect said second endof said inlet bore with said first end of said main bore, and said inletdevice being comprised of an inlet conveyor screw rotating in said inletbore to propel the material to be treated from the first end to thesecond end of said inlet bore.

5. In an apparatus as claimed in claim 4, said inlet conveyor screwhaving an axial core and a helical thread supported thereby, said threadbeing of substantially constant pitch and having a substantially uniformouter diameter substantially equal to the diameter of said inlet bore,and said, axial core having a frustoconical diverging portion adjacentthe second end of said inlet bore in such manner that the materialpropelled by said inlet conveyor screw may be progressively compressedin the form of a substantially airtight plug before reaching saidconnecting canal.

6. In an apparatus as claimed in claim I, said body being formed with anoutlet bore having a first end and a second end, with a materialreceiving canal connecting said second end of said main bore with saidfirst end of said outlet bore, and said outlet device being comprised ofan outlet conveyor screw rotating in said outlet bore to propel thetreated material from said first end to said second end of said outletbore.

7. In an apparatus as claimed in claim 6, said outlet conveyor screwhaving an axial core and a helical thread supported thereby, said threadbeing of substantially constant pitch and having a substantially uniformouter diameter substantially equal to the diameter of said outlet bore,and said axial core having a frustoconical portion adjacent the firstend of said outlet bore, with said portion converging towards saidsecond end of said outlet bore in such manner that the treated materialforced into said first end of said outlet bore from said second end ofsaid main bore may be compressed in said outlet bore in the form of asubstantially airtight plug.

8. In an apparatus as claimed in claim 1, said main conveyor screwhaving an axial core and a helical thread supported thereby, said threadbeing of substantially constant pitch and having a substantially uniformouter diameter substantially equal to the diameter of said main bore,and said core of said main conveyor screw comprising a substantiallycylindrical portion with an outwardly diverging portion adjacent saidsecond end of said main bore.

9. In an apparatus as claimed in claim I, said exposing chamber being inthe form of an elongated bore communicating with said main bore and withsaid returning bore through a longitudinally extending lateral slot.

10. In an apparatus as claimed in claim 9, aid body being formed with alip to prevent material propelled by said main screw from being throwninto said exposing chamber by said main conveyor screw under the actionof centrifugal force.

II. In an apparatus as claimed in claim 10, said returning conveyorscrew comprising a plain central portion having a diameter substantiallyequal to the diameter of said bore.

12. In an apparatus as claimed in claim I, said exposing chamber beingin the form of two separate spaces, each communicating with one of theends of said main bore, and said body comprising means to circulate agas between said separate spaces through said main bore.

2. In an apparatus as claimed in claim 1, said returning conveyor screwpropelling the material being treated in the reverse direction withrespect to said main conveyor screw so as to recycle said material fromthe second end of said main bore towards the first end thereof.
 3. In anapparatus as claimed in claim 1, means to cool said exposing chamber soas to condense vapors evolved from the material being treated.
 4. In anapparatus as claimed in claim 1, said body being formed with an inletbore having a first end and a second end, with a material receivinginlet canal opening into said first end of said inlet bore, and with aconnecting canal to connect said second end of said inlet bore with saidfirst end of said main bore, and said inlet device being comprised of aninlet conveyor screw rotating in said inlet bore to propel the materialto be treated from the first end to the second end of said inlet bore.5. In an apparatus as claimed in claim 4, said inlet conveyor screwhaving an axial core and a helical thread supported thereby, said threadbeing of substantially constant pitch and having a substantially uniformouter diameter substantially equal to the diameter of said inlet bore,and said, axial core having a frustoconical diverging portion adjacentthe second end of said inlet bore in such manner that the materialpropelled by said inlet conveyor screw may be progressively compressedin the form of a substantially airtight plug before reaching saidconnecting canal.
 6. In an apparatus as claimed in claim 1, said bodybeing formed with an outlet bore having a first end and a second end,with a material receiving canal connecting said second end of said mainbore with said first end of said outlet bore, and said outlet devicebeing comprised of an outlet conveyor screw rotating in said outlet boreto propel the treated material from said first end to said second end ofsaid outlet bore.
 7. In an apparatus as claimed in claim 6, said outletconveyor screw having an axial core and a helical thread supportedthereby, said thread being of substantially constant pitch and having asubstantially uniform outer diameter substantially equal to the diameterof said outlet bore, and said axial core having a frustoconical portionadjacent the first end of said outlet bore, with said portion convergingtowards said second end of said outlet bore in such manner that thetreated material forced into said first end of said outlet bore fromsaid second end of said main bore may be compressed in said outlet borein the form of a substantially airtight plug.
 8. In an apparatus asclaimed in claim 1, said main conveyor screw having an axial core and ahelical thread supported thereby, said thread being of substantiallyconstant pitch and having a substantially uniform outer diametersubstantially equal to the diameter of said main bore, and said core ofsaid main conveyor screw comprising a substantially cylindrical portionwith an outwardly diverging portion adjacent said second end of saidmain bore.
 9. In an apparatus as claimed in claim 1, said exposingchamber being in the form of an elongated bore communicating with saidmain bore and with said returning bore through a longitudinallyextending lateral slot.
 10. In an apparatus as claimed in claim 9, aidbody being formed with a lip to prevent material propelled by said mainscrew from being thrown into said exposing chamber by said main conveyorscrew under the action of centrifugal force.
 11. In an apparatus asclaimed in claim 10, said returning conveyor screw comprising a plaincentral portion having a diameter substantially equal to the diameter ofsaid bore.
 12. In an apparatus as claimed in claim 1, said exposingchamber being in the form of two separate spaces, each communicatingwith one of the ends of said main bore, and said body comprising meansto circulate a gas between said separate spaces through said main bore.